An Intrepretation of AE Aquarii.

The spectrum of AE Aquarii is discussed on the basis of spectrograms taken at the Lick Observatory, giving a dispersion of 13OA mm at HT. The late-type component of this double star, classified on the Morgan-Johnson system, is found to be KS IV-V. This classification, taken together with Joy's minimum value of 10 for the mass of the star, indicates that a rapid evolutionary expansion may already have brought it to the point of filling one lobe of the zero-velocity surface passing through the inner Lagrangian point of the system. On this hypothesis, supported by the presence of narrow Ca ii emission lines, the K star is found to eject material, some of which is collected by the blue companion The order of magnitude of the rate of this transfer of mass is estimated by three independent methods: (1) the theoretical Sandage-Schwarzschild rate of evolutionary expansion; (2) the observed luminosity of the blue star; and (3) the intensities of the narrow and broad emission features in H . These estimates agree, yielding a rate of 1025 g/year. The density of material in the region surrounding the blue star is found to be, accordingly, 10-13 g/cc. It is suggested that the accretion of mass by the blue star is related to the outbursts of 2 mag. found by Zinner, and a possible connection with the U Geminorum type variables is pointed out.